It is often desirable to limit access to enclosed areas through the use of electronically or otherwise controlled access doors or to restrict the operation of equipment or machinery, e.g., computers, copying machines, parking facilities, etc. Automatically limiting access to a selected number of individuals through the use of electronic or mechanical means results in significant economies through avoidance of the need for guards, security personnel or outside security contractors. Moreover, automatic access devices such as that contemplated by the instant invention are extremely flexible and may be used in connection with a variety of applications aside from limiting access to a particular room or area.
In this regard, numerous electronic systems typically using "card keys" or access cards have been developed over the years for industrial and commercial applications. Access cards, typically comprised of a planar layer of barium ferrite, or other similar materials, interposed between sheets of vinyl, stainless steel or other magnetically inert material, are generally used to "key" the system. Specifically, a number or other code is magnetically represented on the face of the barium ferrite layer of the card through a coding system. The card is then inserted, directly or by wiping, or is interposed within a control device adjacent or proximate to an area to be accessed (e.g., a doorway and door) and is electrically linked with the door lock or operating system of the device to be controlled. The slot has a singular or series of sensors, and the sensors are activated to read the encoded magnetic data on the face of the card from the data carrying medium of the card. The sensors work in various ways; for example, some sensors detect changes in resistance or conductance in the presence of a magnetic field. Accordingly, the sensor will typically "read" the series of magnetically encoded points on the face of the card as a binary number, i.e., a series of 0's or 1's.
For example, a typical card might consist of two columns of data points along the card surface. One column serves as the "clock," while the other serves as the encoded data. When the sensor detects a magnetic point in a particular row of the "clock column," the sensor then looks to the data column in the same row to determine whether the point is magnetized or not. If magnetized, the sensor might be thought to interpret that point as a "1" in a series of binary digits. The sensor reads each row of the various columns in an identical manner and ultimately generates a binary number comprised of a series of 0's and 1's.
In the prior art, this binary string is communicated to a programmable microprocessor usually within the main control unit having storage and memory capability and equipped to recognize the binary string and, if appropriate, issue a corresponding command signal, directly or indirectly, to the device to be controlled, e.g., a door lock. The microprocessor may be programmed to grant access (i.e., activate) a particular device to be controlled upon receiving from the sensor a certain number or numbers represented in binary form, while excluding (i.e., deactivating or failing to activate) the device to be controlled in response to still other received binary strings. Accordingly, access or operation may be selectively limited to those having access cards that are appropriately encoded.
In general, electronic access systems have proved to be fairly reliable and secure. Nonetheless, a number of operational problems have been identified. For instance, it is critical that the sensor accurately "reads" the encoded data in the data carrying medium of the access card. Often times, an inaccurate "read" is obtained on account of improper or careless insertion of the access card into the slot containing the sensor or series of sensors for detecting the encoded information or even wearing of the card or mechanical guides directing the card into the slot. Second, security may be breached and the access card circumvented through counterfeiting or unauthorized duplication of access cards, especially critical in high security (e.g., governmental) applications.
For example, in the prior art, data is detected by the sensors as the card is inserted into the access slot. Accordingly, "play" from side to side or uneven insertion can result in a "misread." In response to this problem, the prior art also includes a slot having a switch at its internal end. The switch must be first activated by the edge of a fully inserted card prior to sensing of the encoded data. This solution, of course, results in further complication of the apparatus, as well as additional expense attendant to the switch. Maintenance problems are similarly encountered. Still further, insertion of the card upside down or backwards results in a "misread." In short, a cardholder properly permitted access to the device to be controlled can nonetheless be denied access for failure to properly and carefully insert the access card. This problem remains in the prior art and as yet, has not been adequately solved in an economical and efficient manner.
Counterfeiting or unlawful duplication of access cards has also proved troublesome, especially with regard to high risk and security conscience applications. Accordingly, there have been attempts in the art to disguise data by, for example, altering polarities, reading only certain discrete points on the face of the access card, reprogramming the microprocessor on a regular basis, or exchanging access cards frequently. These efforts, however, have proved inconsequential to an effective resolution of the counterfeiting/duplication problem.
In particular, since many devices are based upon a binary string of numbers, it is extremely difficult to disguise data arranged in only two columns. Moreover, the data density capable of being represented on such a card is low thereby making the access card code easier to decipher, copy or counterfeit. In addition, the low data density results in decreased flexibility in applications requiring a large number of access cards.
Still further, the prior art has also encompassed various systems for improving the "read" accuracy of the devices. For instance, a "two read" system, known in the art, provides for reading of the data after detection of a switch closure or sentinel at the front end of a card and the reading of the card again as it is pulled out of the slot. The two readings are then compared and, if identical, access is granted. When the comparison is identical, there is, of course, a high degree of accuracy and reliability of the reading. However, the "two read" system is prone to a high number of "misreads" attendant to the insertion and excursion of the card from the slot. A "one read" system has also been used in the art. This requires the presence of a switch or sentinel, discussed above, at or near the end of the slot. Side to side movement of the card or play in the insertion of the card, may result in numerous misreads under this system.
Accordingly, the instant invention provides a method and apparatus to improve upon the accuracy of the "reads," as well as allowing the encoded data to be further disguised and protected from unlawful or unauthorized copying or duplication.